Signaling system



June 1932. R. c. CURTIS ET AL 7 1,862,137

SIGNALING SYSTEM Filed July so, 1928 I x i I I l 21% l l l am I m 1- :g L J '5. \1

l l i l i l if: N\\ I I H g o-|||| E l g 1 T T: I N I I I liq Mums, Huh-I m l m l (g I I INVENTORS l Rlchard. GCurfis and l I I Cla 'ence A.Bodd|'e ATTdRNEY Patented June 7, 1932 E PAaNT OFFICE.

RICHARD C. CURTIS AND CLARENCE A. .BODDIE, OF WILKINSB'URG, PENNSYLVANIA,

ASSIGNORS TO WESTINGHOUSE ELECTRIC AND MANUFACTURING- COMPANY, A COR- PORATION OF PENNSYLVANIA SIGNALING SYSTEM Application filed Jul so, 1928. Serial No.'296,163.

Our invention relates to signaling systems, and more particularly to systems of the socalled duplex type, wherein means are incorporated for accomplishing the simultaneous transmission and reception of signals at a single station.

In order that a duplex radio signaling sys- "tem shall be capable of successful operation,

it is necessary to provide means for neutralizing, in the receiving apparatus, the effect of waves which are being transmitted from the same station. It has previously been proposed to derive from the transmitting antenna an electromotive force equal in value and opposite in phase to the potential induced in the receiving antenna by reason of its proximity to the said transmitting antenna, and to impress this force upon the receiving circuit in such manner as to neutralize, in the receiving apparatus, the eifect of theinduced potential. The patent to Alexanderson, 1,318,042, discloses a duplex signaling system of the type referred to.

' In the Alexanderson system, however, and

in other systems of the same general type with which we arefamiliar, the theoretical balance can be obtained only when the transmitter is steadily radiating unmodulatcd high-frequency oscillations. At the instant when modulating frequencies are first impressed upon the transmitter, the balance is destroyed and it cannot subsequently be restored by manual adjustment during the period that the transmitter output is being modulated. As a result of this condition, true \duplex operation has not, previous to our invention, been attained with any conspicuous measure of success.

It is, accordingly, an object of our inventionto provide-an improved radio signaling system of the duplex type.

' Another object of our invention is to provide, in a signaling system of the aforesaid type, improved means for balancing-out the efiect of a local transmitter on local receiving apparatus.

Another object of our invention is to provide, ina signaling system of the aforementioned type, improved balancing means that shall be equally as effective when the transmitter is modulated as when it is unmodulated. 7 I r Another object of our inventionisto provide, in a signaling system of the aforemene tioned type, improved balancing means that" shall be equally as eifective when modulation is abruptly impressed on the transmitteras when the transmitter is radiating unmodulated continuous waves. i

Another and more specific object of our invention is to provide a signaling systemof theduplex type thatv shall be particularly adapted to the transmission and reception of signals by means of high-frequency carriercurrents propagated over metallic conductors.

Although our invention is'equallyas well applicable to space-radio duplex systems as to tems, comprising a plurality of antennae separately coupled to the metallic conductors constituting a high-power transmission line, and having such values of inductance and capacity as to be resonant to both the trans mitting and receiving frequencies. A cou- 'pling system of the type we prefer to employ is disclosed in the copending application of C. A. 'Boddie, Serial No. 134,975, filed Septem 'ber 13, 1926, and assignedtothe Westinghouse Electric and Manufacturing-Company.

The several antennae are serially connected through an inductor to which is coupled the transmitting apparatus, and the receiving apparatus is dilferenti'ally coupled to the antenna system in such manner as to accomplish the objects of our invention, namely, a

complete balance both during the intervals;

when the transmitter ismodulated and during the intervals when modulation is notimpressed thereon. Means may also be included in the balancing circuits for shifting the phase of the balancing potentials, as shown.

in the Alexanderson patent, if desirable, al-

- though, in general, we have found it unnecessary to utilize such phase-shifting devices. .The novel features that we consider characteristic of our invention, are set forth With particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description of a specific embodiment, taken in connection with the acmp ying d ins- The single figure of the drawing is a diagrammatic view of a portion of a carrier- 'current duplex signaling system comprising a preferred embodiment of our invention.

The system illustrated in the drawing comprises a plurality, of metallic conductors 1,

2 and 3 that may be either power lines, telegraph lines, or the like, extending between 7 good results. I

' The antenna a plurality of similar transmitting-receiving stations 4 and'5. fhe station 4 is provided with two couplingantennae 6 and 7 while the station 5 is similarly equipped with two antennae 8 and 10. These antennae areelectrostatically coupled to the metallic conductors by being supported in proximity thereto on poles (not shown), although couplingcondensers "may be utilized with equally as 6 is connected to one terminal i of the secondary winding 11 of a couplingtransformer 12 over-a circuit including a variable inductor 13, a tuned circuit compr sing an inductor 14 and a variable condenser 15,

and a coupling inductor 16; The antenna 7 r is connected tothe opposite terminalof the couplingrtransformer secondary winding 11 o ver a-circuit including a variable inductor 1?, and .a' tuned circuit coniprisingan inductor 18 and a variable condenser 20.- The inductors 13 and 17 and the tuned circuits 1 aforementioned 1 A. Boddi-e.

14 1'5and 18-20 are for the purpose of maid-rig the antenna system simultaneously resonant to both a transmitting frequency and a receiving frequency, as disclosed in the c'opending application of C.

A receiving device 21 has an input circuit comprising a plurality of inductors 22 and 23 connected in series. The inductor 22 is variably coupled to the inductor 16 included in the circuit between the antenna 6 and the coupling transformer secondary winding,

While the inductor 23 is coupled to an inductor 24 which, in series with a condenser 25' anda resistor 26, is connected in shunt t the said secondary winding. v

' An additional series-tuned circuit com prising a variable condenser 27 and an inductor' 2'8 is also connected in shun t to the said secondary winding.

transformer 12 is comprised in the output circuit of a signal-source represented by a rectangle designated transmitter.

The seriesstuned circuit, including the condenser 2i and the inductor 28, is adjusted to -c When, however, modulation is upon the signal source, the time required ed by the expression The primary winding 30; of the coupling.

be resonant to the receiving frequency, while the series-tuned circuit, including theinductor 24, the condenser 25 and the resistor 26, is tuned to the transmitting frequency.

The various elements of the last referred-to circuit are so chosen that the circuit will,-as a whole, have the same time-constant as the antenna-coupling system considered apart from the said circuit.

Inasmuch as a certain definite capacity exists between the antenna-6 and the antenna 7 by reason of their proximity toeach other,

and "by reason of the fact that they are coupled, respectively, to the power lines 2 and 3,

the potentials impressed upon the secondary winding of the coupling transformer from the signal source causes oscillatory currents .to be set up in the circuit which serially in cludes the several antennae and the said intera-ntennarcapacity. The inductors 16 and 22 and the inductors 23 and 24 are so coupled that the said oscillatory currents tend toiieutralize, insofar as theireflect upon the input circuit of the receiving device is concerned, during such times as the oscillatory currents are unmodulated. V

impressed for a'voltage to appear across the inductor 22 is proportional to the time constant of the whole antenna-coupling system. In order. that an equal opposingvoltage shall be. 'bu-il up across the, inductor 23 at the same rate. as that across the inductor 22in seriestherewith, the time-constant of the circuit including the inductor 24:, the condenser 25 and the resistor 26, which constant is representwhere L' site inductance of the inductor 24 and R the valueof the resistor 26, is made the same as that of the antenna-coupling system per se. 'Since it is desirable to keepthe energylossas low as possible in this circuit, R is made large, as is also the inductance L; Accordingly, since the time constants of the circuits from which the balancing voltages are obtained are made equal, the frequency of theoscillatory currents flowing therein has no effect upon the balance obtainable, and the potentials across the inductors22 and 23 are always equal and opposite in phase, irrespective of the presence or absence of modulation.

As previously explained, the series-tuned receiving device is concerned, since the said received currents induce substantially no voltage across the inductor 24.

It is entirely feasible to dispense with the inductor 16 to which the input inductor 22 is coupled, if desirable, and to couple the latter inductor directly to either the inductor 13 or to the inductor 14.

We have also found it advisable to enclose the conductors leading to the receiving device in a grounded shield, in order that they, themselves, shall not function to pick up energy from the signal source.

It is our belief that previous workers in the art to which our invention pertains failed to appreciate the necessity of deriving balancing potentials from a circuit which has the same time-constant as the antenna-coupling circuit itself and that, by reason of such failure, no previously proposed duplex signaling system is entirely satisfactory in operation when the receiving and transmitting frequencies are not widely difierent, and when the power employed for transmission is relatively large.

Cur improved system has the further advantage of remaining in balance even though the receiving and transmitting frequencies may shift from their predetermined values, this import-ant characteristic being the result of obtaining balancing potentials from two circuits having the same time-constant.

Although we have illustrated and described our invention as specifically applied to a carrier-current system, it will be apparent to those skilled in the art that it may be equally as well as applied to duplex systems of the space-radio type. Our invention, therefore, is not to be restricted to the embodiment illustrated, but is to be limited only insofar as is necessitated by the prior art and by the spirit of the appended claims.

We claim as our invention:

1. In a system for the simultaneous transmission and reception of signals, a signal source, means for coupling said course to an energy-conveying channel, said means comprising a plurality of antenna circuits in series relationship to each other, a receiving device, means including a circuit having the same time constant as the combined antenna circuits for differentially coupling said receiving device to said antenna circuits and means for by-passing energy at a reception frequency around said circuit.

2. In a system for the simultaneous transmission and reception of signals, a signal source, means for coupling said source to an energy-conveying channel, said means comprising a plurality of antenna circuits in series relationship to each other, a receiving device, means includinga circuit having the same time constant as the combined antenna circuits for differentially coupling said receiving device to said antenna circuits and means comprising a circuit resonant to a reception frequency for by-passing energy at said frequency around said circuit.

In testimony whereof, we have hereunto subscribed our names.

RICHARD C. CURTIS.

CLARENCE A. BODDIE. 

